1. Field of the Invention
The present invention relates to an image heating apparatus for heating an image formed on a recording sheet with an endless film, and, more particularly, it relates to an apparatus for fixing an image that results in improved surface features of a fixed image.
2. Related Background Art
In the past, fixing apparatuses of the heat roller type have been used to thermally fix an image onto a recording sheet. An image heating apparatus wherein an image on a recording sheet was heated via a thin film has also been proposed, as described in U.S. Ser. No. 206,767 and the like. Since an this image heating apparatus of the film can utilize a heating body having a low heat capacity and can concentrate the heat at a nip area, it is possible to reduce power consumption and to reduce or eliminate the wait time.
If an endless film is used with this image heating apparatus of film type, the deviation or shift of the endless film will occur. However, it is difficult to strictly control such shift of the endless film.
In U.S. Ser. Nos. 712,532, 712,573 and 798,546, a technique is used whereby a film is loosely wound to reduce the shift force of the endless film and the shift of the film is regulated by engaging edges of the endless film by flanges. In such a technique, the film is driven by a pressure rotary member which cooperates with a heating body to form a nip with the film interposed, and the flanges are disposed along the length of the film except for an area corresponding to the nip.
However, when the edges of the film are regulated by the flanges in this way, if the shift force of the film becomes great, the bending, wrinkles and/or crack will occur in the film, with the result that, in the image heat fixing apparatus, the deterioration of the fixed image, the poor running of the fixing film, the reduction of the service life of the film and/or noise due to the film shift regulation will occur.